# Among-population proteomic differences in Schistocephalus solidus based on excretory/secretory and total body protein predictions

## TL;DR

This study finds that the parasitic cestode Schistocephalus solidus has population-specific differences in its excretory/secretory and total body proteins, which may reflect adaptation to different host environments.

## Contribution

The study provides the first evidence of among-population proteomic variation in a helminth parasite's excretory/secretory proteins.

## Key findings

- 1362 total proteins were identified in S. solidus, with 542 found only in excretory/secretory proteins.
- Signaling and transmembrane proteins were detected in ESPs that had not been previously characterized in S. solidus.
- Protein spectrum counts varied significantly among populations, indicating population-level proteomic differences.

## Abstract

Parasites secrete and excrete a variety of molecules that evolved to help establish and sustain infections within hosts. Parasite adaptation to their host may lead to between-population divergence in these excretory and secretory products (ESPs), but few studies have tested for intraspecific variation in helminth proteomes.

Schistocephalus solidus is a cestode that parasitizes the threespine stickleback, Gasterosteus aculeatus. We used an ultra-performance liquid chromatography–mass spectrometry protocol to characterize the ESPs and whole-body proteome of S. solidus. Specifically, we characterized the proteome of S. solidus at the plerocercoid stage from wild-caught stickleback from three lakes on Vancouver Island (British Columbia, Canada) and one lake in Alaska (USA). We tested for differences in proteome composition among the four populations and specifically between ESPs and body tissue.

Overall, we identified 1362 proteins in the total proteome of S. solidus, with 542 of the 1362 proteins detected exclusively in the ESPs. Of the ESP proteins, we found signaling peptides and transmembrane proteins that had not been previously detected or characterized in S. solidus. We also found that protein spectrum counts varied greatly among all lake populations.

These population-level differences were observed in both ESP and whole-body tissue types. Our study suggests that S. solidus can excrete and secrete a wide range of proteins which are distinct among populations. These differences might reflect plastic responses to host genotype differences, or evolved adaptations by Schistocephalus to different local host populations.

The online version contains supplementary material available at 10.1186/s13071-025-06807-x.